meanwhile president obama trying to shake off a lackluster night. in denver for sure. >> still talking about the debate. >>> later, 50 years ago today marking half a century since the fab four's first single changed music and the world. >> talk about timeless songs. absolutely one of them too. wait till you see the kids in the piece. who are like -- what is that? you know, it's like grandpa's music to them. >> itunes, baby. >> that's right, exactly. they will learn one day, right? >>> new developments in the shooting death of a patrol agent. federal investigators are now trying to figure out if nicholas ivy died at the hands of a fellow officer. >> the 30-year-old father of two was shot and killed this week just north of the mexico/arizona border. suspicion immediately fell on drug smugglers, and mexican officials even arrested two men as investigators considered friendly fire. ivy's family is focusing on their loss. >> we've been so preoccupied with the grief of the loss, we really haven't had time to be angry at anything. it is what it is. i won't